The present invention relates generally to rotatable members that are able to achieve balanced conditions throughout a range of rotational speeds. The present invention also relates to methods and systems for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balancing action. The present invention additionally relates to methods and systems in which inertial masses are actively shifted within a body rotating on a shaft in order to cancel rotational imbalances associated with the shaft and bodies co-rotating thereon. The present invention additionally relates to methods and systems for dynamic balancing, utilizing a data manipulation method to achieve a balanced state more quickly.
When rotatable objects are not in perfect balance, nonsymmetrical mass distribution creates out-of-balance forces because of the centrifugal forces that result from rotation of the object. This mass unbalance leads to machine vibrations that are synchronous with the rotational speed. These vibrations can lead to excessive wear and unacceptable levels of noise. Typical imbalances in large, rotating machines are on the order of one inch-pound.
It is a common practice to balance a rotatable body by adjusting a distribution of moveable, inertial masses attached to the body. In general this state of balance may remain until there is a disturbance to the system. A vehicle tire, for instance, can be balanced once by applying weights to it and the tire will remain balanced until it hits a very big bump or the weights are removed. However, certain types of bodies that have been balanced in this manner will generally remain in balance only for a limited range of rotational velocities. One such body is a centrifuge for fluid extraction, which can change the degree of balance as speed is increased and more fluid is extracted.
Many machines are also configured as freestanding spring mass systems in which different components thereof pass through resonance ranges during which the machine may become out of balance. Additionally, such machines may include a rotating body loosely coupled to the end of a flexible shaft rather than fixed to the shaft, as in the case of a tire. Thus, moments about a bearing shaft may also be created merely by the weight of the shaft. A flexible shaft rotating at speeds above half of its first critical speed can generally assume significant deformations, which adds to the imbalance. This often poses problems in the operation of large turbines and turbo generators.
Machines of this kind usually operate above their first critical speed. As a consequence, machines that are initially balanced at relatively low speeds may tend to vibrate excessively as they approach full operating speed. Additionally, if one balances to an acceptable level rather than to a perfect condition (which is difficult to measure), the small remaining xe2x80x9cout-of-balancexe2x80x9d will progressively apply greater force as the speed increases. This increase in force is due to the fact that F is proportional to rxcfx892 (note that F is the out-of-balance force, r is the radius of the rotating body and xcfx89 is its rotational speed).
The mass unbalance distributed along the length of a rotating body gives rise to a rotating force vector at each of the bearings that support the body. In general, the force vectors at respective bearings are not in phase. At each bearing, the rotating force vector may be opposed by a rotating reaction force, which can be transmitted to the bearing supports as noise and vibration. The purpose of active, dynamic balancing is to shift an inertial mass to the appropriate radial eccentricity and angular position for canceling the net unbalance. At the appropriate radial and angular distribution, the inertial mass can generate a rotating centrifugal force vector equal in magnitude and phase to the reaction force referred to above. Although rotatable objects find use in many different applications, one particular application is a rotating drum of a washing machine.
Many different types of balancing schemes are known to those skilled in the art. U.S. Pat. No. 5,561,993, which was issued to Elgersma et al. on Oct. 22, 1996, and is incorporated herein by reference, discloses a self-balancing rotatable apparatus. Elgersma et al. disclosed a method and system for measuring forces and motion via accelerations at various locations in a system. The forces and moments were balanced through the use of a matrix manipulation technique for determining appropriate counterbalance forces located at two axial positions of the rotatable member. The method and system described in Elgersma et al. accounted for possible accelerations of a machine, such as a washing machine, which could not otherwise be accomplished if the motion of the machine were not measured. Such a method and system was operable in association with machines not rigidly attached to immovable objects, such as concrete floors. The algorithm disclosed by Elgersma et al. permitted counterbalance forces to be calculated even when the rotating system (such as a washing machine) was located on a flexible or mobile floor structure combined with carpet and padding between the washing machine and a rigid support structure.
U.S. Pat. No. 5,561,993 thus described a dynamic balance control algorithm for balancing a centrifuge for fluid extraction. To accomplish such balance control, sensor responses to balancing control actions on a centrifuge were modeled and utilized to determine control actions that would serve to drive an associated system toward a balanced state. Such a system is generally time variant, such that the control models utilized therein may need to be routinely updated based on the measured response to a previous control action, which is a variation of perturbation theory, well known in the art.
The control algorithm explained in U.S. Pat. No. 5,561,993 also presented a scaling scheme that considered only the threshold-normalized change in sensor value when creating the control model. This did not address issues relating to measurement accuracy and sensor resolution that may result in bad information being supplied to the control model. The creation of control models using poor information may result in poor models that provide inadequate predictions. Based on the foregoing, it can be appreciated that these sensor-related issues can lead to lengthy balancing times and the inability to obtain maximum spin speeds in centrifuge environments, such as, for example, a washing machine, and that improved balance times can be achieved by addressing these issues.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is one aspect of the present invention to provide methods and systems in which rotatable members can achieve balanced conditions throughout a range of rotational speeds.
It is another aspect of the present invention to provide methods and systems for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balance action.
It is still another aspect of the present invention to provide methods and systems for dynamic balancing rotatable members through a method of data manipulation whereby responses to control actuator actions are either accentuated or diminished such that a balanced state is achieved in a shorter period of time.
In accordance with various aspects of the present invention, methods and systems are disclosed herein for dynamically updating a control model for controlling a balance state of a rotating device or rotating system. Sensor responses can be utilized to define a control model that, along with sensor measurements, can be used to determine control actions that drive the rotatable apparatus to a balanced state and provide new sensor responses.
This invention provides a simple strategy for data manipulation that improves the information used to create the control model, thus improving the effectiveness of the control model, so as to decrease balance times and reduce the possibilities of not attaining the maximum spin speeds. The critical components of this invention include zeroing sensor measurements and changes in sensor measurements below some multiple of the sensor error band and sensor noise floor. Other critical components of the invention involve applying scaling factors to certain sensors to emphasize and de-emphasize certain sensors based on the current operating conditions of the system. The method that is presented for dynamically manipulating the data may be used to force the control system to pay closer attention to certain sensors either for safety reasons or to force the algorithm to converge faster.
The collection of these methods and systems ensures that good data is used to create the control model and that critical inputs are given priority in making control model updates. Both of these factors lead to a more accurate control model under changing system conditions and thereby lead to decreased balance times and facilitating the achievement of maximum spin speeds in a rotating system.